title: Treatment with gefitinib or lapatinib induces drug resistance through downregulation of topoisomerase IIα expression.
abstract: The EGF receptor (EGFR) is therapeutically targeted by antibodies and small molecules in solid tumors including lung, colorectal, and breast cancer. However, chemotherapy remains important, and efforts to improve efficacy through combination with targeted agents is challenging. This study examined the effects of short and long durations of exposure to the EGFR- and HER2-targeted tyrosine kinase inhibitors (TKI) gefitinib and lapatinib, on induction of cell death and DNA damage by topoisomerase IIα (Topo IIα) poisons, in the SK-Br-3 HER2-amplified breast cancer cell line. Short exposure to either gefitinib or lapatinib for 1 hour did not affect the induction of apoptosis by the Topo IIα poisons doxorubicin, etoposide, and m-AMSA. In contrast, cells treated for 48 hours were resistant to all three drugs. Short exposure (1 hour) to TKI did not alter the number of DNA single- or double-strand breaks (DSB) induced, whereas longer exposure (48 hours) reduced the number of DNA DSBs and the formation of γ-H2AX foci. Both gefitinib and lapatinib reduced the expression and activity of Topo IIα at 48 hours. Studies using a cell line with inducible downregulation of Topo IIα showed that expression of Topo IIα, and not Topo IIβ, determined the number of DNA strand breaks induced by these chemotherapeutic agents. These results indicate that prolonged exposure to TKIs targeting EGFR and HER2 induce resistance to doxorubicin, etoposide, and m-AMSA through downregulation of Topo IIα. This may explain why their addition to chemotherapy regimens have not increased efficacy.
authors.affiliation: Corresponding Author: Daniel Hochhauser, UCL Cancer Institute, Paul O'Gorman Building, University College London, 72 Huntley Street, London WC1E 6BT, UK. D.hochhauser@ucl.ac.uk.
authors.forename: Jaishree
authors.initials: J
authors.lastname: Bhosle
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Kiakos
authors.forename: Andrew C G
authors.initials: AC
authors.lastname: Porter
authors.forename: Jenny
authors.initials: J
authors.lastname: Wu
authors.forename: Andreas
authors.initials: A
authors.lastname: Makris
authors.forename: John A
authors.initials: JA
authors.lastname: Hartley
authors.forename: Daniel
authors.initials: D
authors.lastname: Hochhauser
mesh_terms: D000677:Amsacrine / Q000494:pharmacology; D000951:Antigens, Neoplasm / Q000235:genetics*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005047:Etoposide / Q000494:pharmacology; D000077156:Gefitinib; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006657:Histones / Q000235:genetics; D006801:Humans; D000077341:Lapatinib; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011799:Quinazolines / Q000494:pharmacology*
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D000677:Amsacrine; D000077341:Lapatinib; D005047:Etoposide; D004317:Doxorubicin; D004250:DNA Topoisomerases, Type II; D000077156:Gefitinib